Welding guns of the type having a replaceable tip and an axial passage through which a welding wire extends are in wide usage, particularly in automatic or robotic welding machines. The welding wire typically is fed through the welding gun and the tip from a coil of such wire. Although that portion of the wire which extends through the tip is substantially straight during its passage through the tip, that portion of the wire which projects beyond the tip tends to retain some residual curvature as a result of its being withdrawn from a coil. The residual curvature of the wire causes it to bear against the edge of the tip defining the wire-accommodating passage. Since the welding wire usually is formed of metal which is harder than that forming the tip, movement of the wire through the tip soon causes the wearing of a groove in the tip adjacent its free end. Such groove causes that portion of the welding wire which extends from the free end of the tip to occupy a position to one side of the longitudinal axis of the tip. Consequently, movement of the tip toward an article to be welded causes the free end of the welding wire to engage the workpiece at a position to one side of the intended point of engagement. This results in inaccurate welding and, in some instances, improper welding of the workpiece.
Another problem encountered with conventional welding tips of the kind referred to is that repeated welding operations using a welding wire that is not accurately located with respect to the workpiece can result in arcing between the welding wire and the tip and electrical discharge machining of the tip adjacent the passage through which the welding wire extends. Such machining is undesirable inasmuch as it further deforms the wire-accommodating passage in the welding tip, thereby introducing further errors in the positioning of the free end of the welding wire with respect to the workpiece that is to be welded.
The problems associated with conventional welding tips are well known. However, there does not appear to have been any real solution proposed to the problems other than that of periodically replacing a worn welding tip with a new one so as to overcome for a limited time the disadvantages flowing from a laterally displaced welding wire. In some factories welding tips are replaced at the beginning of each shift by the person or persons responsible for the welding operations. Although conventional welding tips are not expensive, the time required to replace the tips, coupled with the consequent unproductive time of the welding machine during tip replacement, represents significant costs.
The object of the present invention is to provide a welding tip which overcomes the disadvantages described above, thereby greatly extending the useful life of such a welding tip.